1. Field
The present embodiments relate to a thin film transistor, and more particularly, to a thin film transistor including an HfInZnO-based oxide semiconductor layer as a channel layer, a method of manufacturing the same, and an organic electroluminescent device including the same.
2. Description of the Related Technology
A thin film transistor (TFT) is a special type of a field effect transistor made by depositing thin films of a semiconductor material over an insulating supporting substrate. The TFT basically includes three terminals, e.g., a gate, a drain, and a source, and is mainly used as a switching device.
Currently, commercially available products, such as notebook computers, PC monitors, TVs, mobile devices, and the like mostly include amorphous silicon thin film transistors (a-Si TFTs). Amorphous silicon may be deposited over large areas and easily deposited at low temperatures onto a glass substrate, and thus is most widely used in TFTs. However, as the requirements for display devices with larger sizes and higher image quality have increased, high performance thin film transistors having higher electron mobility than a-Si TFTs, e.g., 0.5 to 1 cm2/Vs, and appropriate manufacturing techniques have been required.
Polysilicon (poly-Si) TFTs have a mobility of several tens to hundreds of cm2/Vs, and thus a data driving circuit or periphery circuit required for higher mobility may be embedded in a substrate. In addition, channels of such TFTs may be made short, and thus an aperture ratio of a screen may be high. Moreover, poly-Si TFTs may have high resolution, operate at low driving voltages, have low power consumption, and have less characteristic deterioration. However, a crystallization process used to manufacture poly-Si TFTs is complicated, and thus additional manufacturing costs may increase. In addition, due to technical problems such as manufacturing equipment limitations or uniformity defects, manufacturing of a large-scale substrate using poly-Si TFTs has not been realized up to date.
Oxide semiconductor devices have advantages of both TFTs and poly-Si TFTs. The oxide semiconductor devices may be manufactured at a low temperature, easily be made in large sizes, and have high mobility and a excellent electric characteristics like the poly-Si TFT. Thus, research is currently being conducted in order to use an oxide semiconductor layer in a channel area of a TFT.
However, recent reports have disclosed that the characteristics of commonly used InGaZnO oxide semiconductor devices deteriorate when exposed to plasma or external agents (for example, moisture, oxygen, or the like). Also, to protect the oxide semiconductor layer, an etch stop layer is disposed on the oxide semiconductor layer. However, depending on the conditions for forming the etch stop layer, the characteristics of the oxide semiconductor devices may severely deteriorate. In addition, the condition ranges wherein the characteristics of the oxide semiconductor devices do not deteriorated are limited, and thus there is a need for fundamental changes in oxide semiconductor devices.